Validation and Prediction of the Temperature-Dependent Henry's Constant for CO2-Ionic Liquid Systems Using the Conductor-like Screening Model for Realistic Solvation (COSMO-RS)

Henry's constant H of carbon dioxide in a number of ionic liquids (ILs) has been studied using the predictive method COnductor-like Screening MOdel for Realistic Solvation (COSMO-RS). Experimental H values for 14 CO2-IL systems spread over a temperature range of (283 to 333) K have been used to estimate the parameters lambda(1) and lambda(2) of the combinatorial term to calculate the chemical potential. The H values of CO2 in 18 other ILs have been validated and found to be in good agreement with the experimental data with a relative deviation of less than 10 %. Cation groups like imidazolium, pyridinium, ammonium, uronium, thiouronium, and phosphonium have been studied. A total of 12 anions such as L-, BF4-, EtSO4-, TFA(-), OctSO(4)(-), Tf2N-, mFAB(-), eFAB(-), mFAP(-), eFAP(-), pFAP(-), and bFAP(-) were studied to find the most favorable cation and anion combination for high CO2 solubility. It was observed that increasing the fluorination of organic anions containing fluoro alkyl groups gave lower Henry's constant values (following the trend TFA(-) > Tf2N- > mFAB(-) > eFAB(-) > mFAP(-) > eFAP(-) > pFAP(-) > bFAP(-)), thus showing higher CO2 solubility. Among the cations studied, phosphonium-based cations are found to be most promising for higher solubility. It was observed that the entropic effects (combinatorial) arising due to the size and shape of ILs play a major role in the estimation of H values, whereas the enthalpic effects (residual) arising due to molecular interactions have a minor but significant role. A correlation has been developed to predict the H of the [R(n)mim](+) cation-based IL by considering a reference value H-2 of [R(2)mim](+). A common predictive equation has been developed to determine the temperature-dependent H values of CO2 in any cation/anion combination of ILs.